As the size of a substrate changes with its temperature, a difference between substrate temperature and the temperature within a climate chamber of a metrology machine causes the substrate to change its size while sitting on the stage of the metrology machine. If a substrate is not fully temperature-adjusted before measurement starts, this change in size leads to distorted measurement results.
The prior art measurement process is designed to wait for the substrate to become almost fully temperature-adjusted. This means the effect of a temperature difference between the climate chamber and the substrate is small enough to be ignored and does not have any effect on the measurement results of two consecutive measurement loops. The temperature match of the climate chamber and the substrate is determined by repeated measurement of two points or structures on the substrate. When the change in distance between two consecutive measurements is smaller than a given threshold, the substrate is considered to be fully temperature-adjusted.
The time required for a substrate to become fully temperature-adjusted primarily depends on the difference between the substrate temperature and the temperature within the climate chamber or temperature at the stage. It does not depend on the number of measurement sites. This means that for a measurement recipe (measurement process) with only a small number of measurement sites the overhead required for temperature adjustment is large compared with the time required for measuring the sites on the substrate. So, the time required for temperature adjustment is the main driver for limited throughput of substrates in a metrology machine.
It is an object of the present disclosure to provide a method for measuring positions of structures on a substrate which shows an increased throughput.